It is common practice to use, for certain irrigations, so-called “drip” pipes. These are pipes whose wall is pierced, at intervals fixed beforehand, with holes of small diameter through which the water flows into the ground. In order to control the flow from the holes with precision, a flow limiter, commonly called a “dripper” and formed of a hollow plastic part bonded to the inner wall of the pipe, is provided facing each hole. This part has, on the side turned towards the inner wall of the pipe, a hollow part that forms a collecting chamber. This collecting chamber is connected to the inner space of the pipe by a conduit forming a labyrinth formed by a pre-prepared groove on the cylindrical face of the drip, which is intended to be turned towards the inner face of the pipe.
In drip irrigation pipe manufacturing installations like, for example, that disclosed in EP Patent Application No. 0 970 602, drippers are fed regularly into an extrusion station comprising extrusion, calibrating and welding means from a feed device such as a centrifugal bowl and orientator for feeding the drippers according to a determined orientation. In the extrusion station feed by plastic material melted in a melting chamber, the pipe is continuously formed by an extrusion head, calibrated, and the drippers are welded at regular intervals to the inner wall of the still warm pipe so that they adhere to the latter by melting locally. Once the pipe-dripper assembly has cooled in a water cooling tank, a hole is pierced in the wall of the pipe, facing the collecting chamber.
According to this document, the drippers are brought into contact with the pipe and welded thereto using a guide support which penetrates and passes through the extrusion station to extend into the cooling tank, in which a device is provided for pinching the dripper-pipe assembly between the guide support and a belt moving substantially at the speed of progression of the pipe. Welding thus occurs downstream of the melting chamber and the calibrator in the cooling tank. At this point, the pipe has already cooled down greatly, such that the weld between the dripper and the pipe can exhibit imperfections. In order to overcome this problem it is common to overheat the plastic material so that its temperature is still sufficiently high at the point when the drippers are welded. The material is thus brought to a temperature close to its molecular degradation limit. Slight temperature variations can then cause deterioration in the quality of the material, which involves very strict control of the heating temperature, and consequently, an increase in the production costs. Another solution that avoids overheating the plastic material consists in heating the drippers themselves prior to putting them into contact with the pipe. In order to do this, the guide support is provided with a heating resistor. This solution, however, involves significant extra space, complication and increased cost.